Long Exposure Shots on Nikon D3100?

Hi, I saw a picture on facebook where someone did an infinity sign with a sparkler using long exposure. How do you do it! Can someone please explain it to me simply? Everywhere I looked its either not for my camera type or way to complicated! Lol.

Get a tripod and put your camera in either manual or shutter priority mode. Shutter priority mode will take care of the fstop for you.

Then set the shutter speed to several seconds. You might also want to try dialing the exposure compensation down a couple of stops.